(P-TS-14) Anti-D Alloimmunization Rate Following the Transfusion of RhD-Positive Apheresis Platelets to RhD-Negative Patients: A Retrospective Study.

The risk of alloimmunization against the D antigen in patients who are RhD-negative and received RhD-positive platelets is controversial. Historically, platelets were typically derived from whole blood, but are now more commonly collected by apheresis. Apheresis platelets contain a much lower volume of residual red blood cells (0.00017-0.009 ml approximately) as compared to whole blood derived platelets which may contain up to 0.036 ml. Thus, red blood cell content in apheresis platelets is below the threshold (0.03 ml) believed to cause alloimmunization. Therefore, the risk of alloimmunization following transfusion of Rh-D incompatible apheresis platelets may be minimal. Currently, some institutions administer RhIG as prophylaxis against anti-D alloimmunization or will only transfuse RhD-matched platelets to patients, which can cause delays to transfusion and challenges to inventory management. This retrospective study aims to analyze anti-D alloimmunization rate in Rh-D negative patients following transfusion of RhD-positive apheresis platelets at an academic level 1 trauma center.

Study

Design/Methods:

A single center retrospective review of records from all RhD-negative patients who received RhD-positive leukoreduced apheresis platelets from June 2021 to October 2023. Only patients with a documented antibody screen before and after transfusion were included. Patients with a previous history of anti-D, those who received RhD-positive red cells, pregnant women with passive anti-D, and infants were excluded.

Results/Findings:

Two hundred RhD-negative patients met the criteria of the study (Table 1). Total of 1295 RhD-positive apheresis platelet units were transfused to the 200 patients during the period of the study. Median number of transfused units per patient was 2 units (range: 1-121 units). Median serological follow up of these patients was 62 days (range: 1-893 days). None of the 200 RhD-negative patients included in this study developed anti-D following transfusion of RhD-positive apheresis platelets till their last serological follow up. Given the variability of our patient population in regards of age, diagnosis, and rate of transfusion; the absence of anti-D alloimmunization in these patients may support the practice of transfusing RhD-incompatible apheresis platelets to RhD-negative patients.

Conclusions:

Results of this study add more evidence to previously published data that the risk of anti-D alloimmunization following transfusion of Rh(D)-positive apheresis platelets to Rh(D)-negative patients is negligible. This will help transfusion services better manage their platelets inventory and possibly decrease the use of RhIG in these patients.